1. Field of the Invention
This invention relates to phenolic resin based laminate materials endowed with a reinforcement. It also relates to a process for making these laminate materials.
2. Discussion of the Background
Laminated materials are materials having several successive alternating layers or strata of resin which can be thermohardened, whether reinforced or not. Such materials find various applications, notably in construction. They may be used as cladding panel elements, replacing sheet metals which are susceptible to oxidation.
There are known preparations for reinforced phenolic resin based laminated materials. The most widely used phenolic resin is a resol i.e., a resin which can be thermo-hardened, and is obtained by condensation of phenol and formaldehyde (with an excess of formaldehyde) in a basic medium. The hardening of the resin thus prepared, i.e. its cross-linking in a three-dimensional network, is effected by condensation polymerization through the use of an acid catalyst. For example, chlorhydric, sulfuric, phosphoric, oxalic acid, or an aren-sulfonic acid such as benzene sulfonic, phenol sulfonic acid, etc . . . may be used.
Generally a reinforcement in the form of fibers is used, such as cellulose fibers or glass fibers. A reinforcement in non-woven form, for example, a reinforcement of high molecular weight polyester, or a polyvinyl chloride is also possible. Alternatively the reinforcement may be in a fiberglass mat or in a woven form. For example, a reinforcement made of aromatic polyamide, glass or asbestos.
Phenolic resin based laminate materials are sought particularly for their excellent tolerance to fire. But it is equally appropriate that they have the proper surface characteristics, namely, a smooth and homogeneous aspect which does not change over time.
The aspect properties of laminated materials in general and more specifically reinforced phenolic resin based laminated materials are closely related to the process by which they are prepared. Various procedures are known for the preparation of these materials, but up to the present the surfaces of the materials prepared have not had the desired smooth and homogeneous aspect.
According to one procedure, a textile or non-textile that is a woven or non-woven reinforcement is impregnated with resin. The impregnation is finished either by roller or by press and several layers of the impregnated reinforcement are put together. According to a variation of this process, the laminate material is prepared by rolling a resin-impregnated fiber.
According to another procedure, a reinforcement in the form of fibers is projected on a layer of resin on the surface of a mold. The depositing of resin and fibers is repeated as many times as necessary to obtain the desired thickness.
It has been noted that the surface of the materials produced according to these processes is not smooth. Tiny pits form and the fibers mark the surface, leaving their imprints. In addition, the phenomena tend to become aggravated due to aging under the effects of erosion, heat and light. The color of the material changes to dark brown and micro-cracks, crackling and exposure of the fibers occurs after a few months. If one attempts to cover up these defects by directly applying a coating such as a polyurethane bonding material based paint to the materials to form a finishing layer, the material obtained still presents an unaccetably poor surface. The only way to obtain a smooth surface is by applying a pore sealing product such as a polyurethane resin to the laminate material and by sanding the resultant surface before painting it. This involves time-consuming operations.
According to another process, molded articles made of phenolic resin are produced by depositing or projecting, on the surface of a mold, a layer of a synthetic resin-based compound. This compound is allowed to harden at least partially before one or several layers of reinforced resin are deposited on it, according to one of the aforementioned processes. This layer deposited on the mold is currently called gel-coat. According to another variation of this "gel-coat" technique, the gel-coat is deposited or projected on a continuously fed cellulose or thermoplastic film. The resin is deposited on top and covered before it has hardened with another film made of cellulose or another material. This is also covered with a gel-coat; the laminate product being shaped continuously while it hardens. This procedure is particularly adapted to the preparation of thin laminate materials of about 1 millimeter.
The gel-coat technique was developed essentially for the preparation of reinforced resin-based polyester laminate materials for which the gel-coat itself is a polyester resin based coating and the results obtained are satisfactory. It was then attempted to apply this technique to the preparation of reinforced phenolic resin based laminate materials utilizing a phenolic resin-based gel-coat. But the same undesirable phenomena as those described in relation with the preceding processes appeared. With a relatively thin gel-coat, the surface of the material has micropits and fiber imprints. Microprints and fiber imprints can be eliminated by depositing a phenolic resin-based gel-coat in the form of a thicker coating, but, in this case, micro-cracks a crackling occurs.
Thus, one sought to apply unsaturated polyester resin based gel coats to phenolic laminate products to promote proper tolerance to aging of the hardened polyester resins. But conventional formulas for the unsaturated polyester resin-based gel-coats are not compatible with phenolic resins.
To make the two resins compatible, it was proposed, for example, in the publication of French Pat. No. FR 2 331 587, to place a sprinkling of boronic derivatives between a polyester resin gel-coat and the phenolic resin. However, on the one hand, adherence is not entirely satisfactory with this method. And on the other hand, effecting a fine and regular sprinkling is a delicate operation.
It was also proposed, in the publication of French Pat. No. FR 2 447 275, to utilize a furanic resin based gel-coat. But such a gel-coat decomposes over time, thus requiring the application of an additional coating of paint.
It was also proposed to place a furanic resin based gel coat between a polyester resin based gel-coat, serving as the aspect or finishing layer, and the phenolic resin. But furfural, from which furanic resin is derived, has the tendency to migrate into the external polyester resin-based layer. This phenomena provide the desired adhesion between the resins, but still requires the placement of two additional layers on the phenolic laminate.
Accordingly there is a strongly felt need for a phenolic resin-based laminate material possessing smooth and homogeneous surfaces. The surface of these laminate materials should not change upon exposure to light, develop micro-cracks, crackling and exposure of the underlying fiber after time. Such a laminate material should also be facile to prepare.
SUMMARY OF THE INVENTION
Accordingly, it is an object of this invention to provide a phenolic resin-based laminate material possessing a smooth surface.
It is another object of this invention to provide a phenolic resin-based laminate material possessing a homogeneous surface.
It is another object of this invention to provide a phenolic resin-based laminate material which does not suffer from tiny pit formation on the surface.
It is another object of this invention to provide a phenolic resin-based laminate material in which the surface does not suffer erosion upon exposure to heat or light.
It is another object of this invention to provide a phenolic resin-based laminate material in which the surface does not change color upon exposure to heat or light.
It is another object of this invention to provide a phenolic resin-based laminate material in which micro-cracks are not formed on the surface.
It is another object of this invention to provide a phenolic resin-based laminate material in which crackling does not form on the surface.
It is another object of this invention to provide a phenolic resin-based laminate material in which the fibers do not become exposed on the surface after time.
It is another object of this invention to provide a phenolic resin-based laminate material in which the additional layers can be very thin while nonetheless retaining the desired properties; good tolerance to fire, good resistance to aging, good superficial hardness and a smooth surface.
This invention has as an object providing phenolic resin based laminate materials which can be cross-linked by acid catalysis, endowed with a reinforcement, and having at least two surfaces. On at least one of their surfaces, these laminate materials have at least one additional non-phenolic resin based layer. And these laminate materials present none of the aforementioned drawbacks. More specifically, the invention provides such a laminate material for which the additional layer(s) can be as thin as about 1/10th of a millimeter, and which nonetheless retain the desired properties, i.e., good tolerance to fire (classification M1 on the epi-radiator), a sound resistance to aging, good superficial hardness and a smooth surface.
The inventors have now surprisingly discovered a novel phenolic resin-based laminate material which satisfies all of the above objects of this invention. This phenolic resin-based laminate material which can be cross-linked by acid catalysis and endowed with a reinforcement, comprises at least two surfaces. It has on at least one of the surfaces at least one additional layer which is non-phenolic resin based. This phenolic resin based laminate material is characterized in that the additional layer in contact with the phenolic resin is obtained from a formula including an unsaturated polyester resin, a cross-linking solvent for the resin, and possibly one or several other additives. At least one of the components of the formula possesses a hydrophilic center in a number which is at least equal to the number of unsaturation centers of the polymeric chain of the polyester resin.